What should I do about this impurity

Assalamualaikum During an exam, I was desperate for the toilet but I thought I could hold it in until the end of the exam. I ended up wetting myself and I didn't tell anyone because I was too embarrassed. The next day I had an exam in that same seat so I got some wet tissue and wiped over the chair a few times as at the time I thought this was a permissible way to remove the impurity. I recently read on a few websites that this is permissible to do so on smooth surfaces. However, some websites say you have to pour water on it. Once all the exams were over, the chairs got moved to different rooms and there were hundreds of these chairs so it is literally impossible for me to know which chair could have a potential impurity on it. I really need advice as I'm unsure what to do in this situation. A response would be appreciated, Jazakallah Khair.